The sentence that uses an antonym clue to help the reader determine the meaning of the underlined word is the second option: "The former king was adored by the people for his reasonable decisions, but the new king was disliked for his arbitrary decisions."
Antonym is defined by the dictionary as a word that means the opposite of another word,
In this sentence, the word "but" introduces the antonym which will create a contrast ir opposition between the first and the second part. In the first one the word adored is mentioned and in the second, the word disliked works as its antonym.